Existing thin-film-based sensors can be used to sense a multiplicity of environmental factors. Many of these sensors are based on changes to the sheet resistance of the thin film. The interrogation of these sensors is usually done using a hard-wired measuring unit, such as an electrical signal (voltage or current). This signal is usually transmitted via a physical electrical connection to a processing unit, which in turn analyzes and/or transmits the data wirelessly to a receiving unit. These conventional systems can be small in size and portable but require wired connections for their interrogation unless complex wireless capabilities are integrated within the system.
A device that uses a monopole or dipole antenna to monitor corrosion has been presented in US2014/306725 A1. This device does not use a thin-film configuration and its sensitivity can only by adjusted by the tapered shape of the antenna. It is also exclusively related to corrosion and does not include sensing of other stimuli.
Wireless transmission of CNT-based sensors is usually carried out by a microprocessor, which measures and transmits the signal, adding system complexity and power consumption as presented in US2015/0338524 A1.
Autonomous wireless solutions generally introduce a CNT-based element to the transmitting antenna in order to indirectly affect the transmitting signal of the antenna. One solution loads a metal-based antenna with a CNT-based patch to change the resonant frequency of the antenna, US2013/0230429 A1. Others, such as Ong et al. 2002, have proposed a passive capacitive-sensitive sensor based on changes to the permittivity constant of a CNT-based material which can be wirelessly interrogated.
The art currently lacks an “all-in-one” wireless sensor where the change in the sheet resistance of the thin-film sensor material causes a simultaneous attenuation of the wireless antenna signal, for example, a thin-film of nanomaterials which can show dramatic changes in sheet resistance, which directly impacts the wireless signal.